Describes approach based on the Predicted Mean Vote concept as a suitable index of discomfort for housing with evaporative cooling. This index accounts for all important environmental factors and in addition allows dynamic modelling of human responses to the thermal environment, such as adjusting clothing levels and metabolic rate. The computer program TEMPAL is used to predict internal environmental conditions within a dwelling. TEMPAL is shown to be sufficiently accurate for this purpose by comparing predictions with monitored conditions. Using this technique the thermal conditions produced by evaporative and refrigerative cooling plant are compared.